The present invention relates to vehicle transmissions, especially with automatic gear shifting, and more particularly to a device for preventing the engagement of combinations of tooth clutches that would block the shafts of the transmission.
The conventional stepped transmission for rear-wheel drive vehicles can be regarded as a robust, compact and cost-effective product. A typical example of such a lay-out is shown in FIG. 2 in DE10242823A1. An input shaft is coaxial with a main (output) shaft and parallel with a countershaft. A gearwheel that is rotationally fixed on the input shaft meshes with a gearwheel that is rotationally fixed on the countershaft. Several pairs of meshing gearwheels are then located side by side. In each of these pairs, one gearwheel is coaxial with the countershaft; the other is coaxial with the main shaft. One of these gearwheels is rotationally fixed on its coaxial shaft. The other gearwheel; the loose gearwheel, is free to rotate relative to its coaxial shaft, but can be rotationally locked to the shaft by a mechanical tooth clutch. This construction is used for manually shifted transmissions as well as for automated mechanically engaged transmissions, AMT: s. Because of the mechanical tooth clutches, there will during the shift be an interruption of the power transfer between the engine and the driven wheels of the vehicle. Thus, this type of transmission is not power-shifting.
If the loose gearwheels in two gearwheel pairs at the same time would be locked rotationally to their shafts, the transmission would be blocked and the shafts therein could not rotate. This could lead to damage, e.g., broken gear or clutch teeth, and must be prevented. In manual transmissions, the dominant “H-type” shift pattern enables straightforward design of the shift control system to prevent blocked shafts. In AMT: s, blocked shafts can be prevented by proper software, at least under normal conditions. However, in case of faults, e.g., on sensors and/or valves, blocking of shafts could possibly occur. In some designs, this is prevented by designing the automatic shift actuation system similar to a manual one, with one actuator corresponding to longitudinal motion of the shift lever and one actuator corresponding to sideways motion. Such a design might in addition reduce the number of components, but is, in general, not able to allow as quick shifts as a system with one actuator for each tooth clutch. In order to prevent blocked shafts, those latter systems often have an interlocking pin between grooves in the shift actuation parts of two tooth clutches. The length of this pin is adapted to allow one tooth clutch, but not both, engaged. This is a simple, robust and cost-effective design.
Dual clutch transmissions are an interesting crossbreed between power-shifting planetary transmissions and conventional stepped transmissions with power interruption at gear shifts. In principle, a dual clutch transmission has two input shafts, each connectable with a friction clutch to the output shaft of the engine. Functionally, this is equivalent to having two conventional transmissions in parallel and using one at a time for power transfer. The parallel transmission that is not used, idling, for the time being, can have a gear engaged and prepared for a subsequent shift. This shift is carried out by simultaneously disengaging the friction clutch of the previously used parallel transmission and engaging the friction clutch of the previously idling parallel transmission.
When properly designed, dual clutch transmissions have a potential of providing power-shifts at a reasonable production cost and low power losses. This is due to the fact that the rotating parts, i.e., gearwheels, shafts and tooth clutches, are similar to those in conventional stepped transmissions. This, furthermore, enables the use of the same production equipment. So, it makes sense to produce dual clutch transmissions in the same facilities as used for conventional stepped transmissions.
Dual clutch transmissions for rear wheel drive vehicles often have two separate countershafts, one connected to each input shaft. One example is found in U.S. Pat. No. 5,150,628. These countershafts make the transmission considerably wider than a conventional stepped transmission. That may lead to difficulties in installing the transmission into the vehicle. However, in some dual clutch transmission designs there is only one countershaft, e.g., as in DE923402, DE3131156A1 and DE102005044068A1. On such a countershaft there are loose gearwheels arranged that can be rotationally connected to each other and to the countershaft by means of mechanical tooth clutches. In a way, this can be regarded as if the second countershaft is arranged coaxial to the first one. The result will be a power-shiftable dual clutch transmission that is not wider than a corresponding conventional stepped transmission. However, the tooth clutches on the countershaft make it more difficult to prevent blocking of shafts. Often, some combinations of the states of three or four tooth clutches may give blocked shafts, whereas other combinations are used for ordinary power transfer. Similar conditions can be found also for dual clutch transmissions that have two separate countershafts. An effective way to prevent blocked shafts in such complex transmissions is to use shift barrels for controlling the tooth clutches, e.g., as in U.S. Pat. No. 5,966,989. Unfortunately, shift barrels normally only allow sequential shifting, i.e., from one gear to the adjacent higher or lower. Multi-step shifts are not possible, in general. Another alternative is to use an active shift blocking system, e.g., as in U.S. RE39598E. That would, however, increase the complexity and cost significantly.
US2009139355 discloses a dual clutch transmission with means for blocking gear changes. The transmission may include: a control bar including a hole; a first shift rail and a second shift rail that are respectively disposed along the control bar; first springs biasing the first rail and the second rail respectively; a first stop and a second stop that are mounted in respective inner grooves of the first rail and the second rail; second springs that elastically support the stops and insert the stops into the hole according to the movement of the rail's. Spring loaded stops will engage with one of the shift forks in a predetermined fork position in order to prevent an undesired gear shift. However, these means only prevent undesirable states of two tooth clutches that would give blocking of shafts.
It is desirable to further develop an interlocking device for preventing engagement of forbidden combinations of tooth clutches in a vehicle transmission.
It is desirable to solve the above problem and to provide an alternative system for preventing engagement of forbidden combinations of tooth clutches in a vehicle transmission.
According to a first aspect of the invention, there is provided an interlocking device arranged to prevent at least one forbidden combination of engaged/disengaged positions of three tooth clutch groups in a vehicle transmission, where each tooth clutch group when in engaged position is arranged to rotationally lock a first shaft to a gearwheel or to a second shaft and when in a disengaged position to rotationally unlock said first shaft from said gearwheel or said second shaft, and where for each tooth clutch group a shift rod is arranged to push a tooth clutch in a tooth clutch group between an engaged and disengaged position. The device is characterized in that said interlocking device comprising:—movable elements where each movable element is directed towards one of said shift rods in order to lock one of said tooth clutch groups in said disengaged position;—an interlocking element arranged in the middle of said movable elements; and where a diameter of said interlocking element and lengths of said movable elements are adapted to allow only two of the tooth clutch groups to be engaged simultaneously.
With the invention a more simple, reliable and cost-effective mechanical system to prevent shafts from being blocked by combinations of at least three tooth clutches is achieved for complex stepped non-planetary transmissions.
According to one embodiment of the invention said movable elements are pins movable radially towards said shift rods.
According to one further embodiment of the invention a groove is arranged on each of said shift rods and where each of said grooves is centred with one of said pins when the tooth clutches are in said disengaged position.
According to one embodiment of the invention said movable elements are protruding bars where each of said protruding bar is fixedly arranged on said shift rod.
According to another embodiment of the invention a groove is arranged on each of said protruding bars.
According to one embodiment of the invention said groove comprises at least one ramp that mate with corresponding chamfers arranged on interlocking element.
According to a further embodiment of the invention at least one of said protruding bars comprises a twin arrangement where each of two protruding bars is fixedly arranged on corresponding said shift rod.
According to another embodiment of the invention some of said movable elements are pins and some are protruding bars.
According to one embodiment of the invention each of said tooth clutch groups comprising only one tooth clutch.
According to another embodiment of the invention two tooth clutch groups comprise only one tooth clutch and one tooth clutch group comprises two tooth clutches, and where another interlocking element is arranged to interact with said interlocking element via one of said pins.
According to a further embodiment of the invention said interlocking element is puck-shaped. According to a further embodiment of the invention said interlocking element is instead ball-shaped.